This invention relates to an intraocular lens for the human eye, and, more particularly, to a masked intraocular lens of the type which can be positioned in the anterior chamber, the posterior chamber, or partially in either the anterior or posterior chamber of the eye. The invention also relates generally to postcataract patient care and vision improvement by implanting a masked intraocular lens to replace the removed natural lens.
As a person ages, occasionally a person's eye lens gets cloudy. When this occurs, a person is said to have cataracts. The cataracts eventually cloud the lens so that a person cannot see clearly. When this happens, removal of the lens is required. Commonly, thick glasses have been used for correcting the vision of postcataract patients. However, the glasses have obvious disadvantages associated with the size and weight of the glasses. An intraocular lens (IOL) may be implanted to replace the human lens; however, these lenses generally are only in focus at one focal distance. The present invention circumvents the need for a traditional IOL augmented by bifocal or trifocal spectacles by implanting an intraocular lens which can focus continuously from near to far and in most light conditions.
Attempts to produce an intraocular lens that is focusable at both near and far distances have not been completely successful. In the normal eye the crystalline lens is self-biased toward a spherical shape, that is, toward maximum refraction; for example, for distance viewing it is radially tensioned, and thereby flattened, by relaxation of the ciliary body. However, once the lens is removed, a replacement lens cannot function in this manner. Thus, intraocular lenses that allow the patient near and far focusability must work on a different principle.
In U.S. Pat. No. 4,409,691, entitled "Focussable Intraocular Lens", an intraocular lens that achieves accommodation in response to contraction and relaxation of the ciliary body is disclosed. This lens works on the same principle as a lens in a camera. It achieves adjustment of the focal distance by adjustment of the spacing between the lens and the fovea. The intraocular lens is spring biased towards its distance focus position where it remains so long as the ciliary body remains relaxed. When the ciliary body contracts, it compresses the spring bias, moving the lens away from the fovea to provide accommodation for near viewing. This lens has not been completely successful as it requires precise implantation into the eye. Furthermore, implantation of this device is a more complex procedure than implantation of standard intraocular lenses. In addition, such a lens requires precise quantification of ciliary muscle body power. However, the capability of ciliary muscle is unknown, especially for elderly patients.
A second technique to try to achieve focusing for near and far vision in an intraocular lens implant is disclosed in U.S. Pat. No. 4,636,211, entitled "Bifocal Intra-ocular Lens". This patent discloses an intraocular lens that focuses for near vision in the central portion of the lens and focuses for far vision by a coaxial ring around the central portion. This lens is not completely successful as, when one focuses on a near object, it is slightly fuzzy around the edges due to the far vision coaxial ring. This creates fuzziness for the viewer.
U.S. Pat. No. 4,605,409 entitled "Intraocular Lens With Miniature Optic Having Expandable and Contractible Glare-Reducing Means", teaches an IOL with masking means for reducing the glare associated with an intraocular lens of small dimension. The masking means of that invention does not overcome the problem associated with standard IOLs, that is, it does not improve focusability.
Pinholes have been used in pinhole cameras to bring distant objects, near objects, and everything in between into continuous focus. Pinholes are used by ophthalmologists to assess retinal function; the pinhole acts as a sort of universal lens, correcting all refractive errors, including astigmatism and spherical aberration. Although it has been known that the pinhole acts in this useful way, pinhole contact lenses and pinhole IOLs (such as is described in Choyce, Intra-Ocular Lenses and Implants, London. H.K. Lewis, 1964. pp. 21-26) made in the past did not work in dim light conditions. In adequate light the pinhole contact lenses and the pinhole IOLs functioned as expected, allowing the patient to see in the distance as well as read a book. However, in dim light, where the pinhole fails to admit enough light into the eye, image quality declined. Essentially it was like wearing dark glasses indoors.
An earlier study of pinholes indicated that pinholes might be useful for solving vision problems caused by refractive errors if the problem of vision in dim light could be overcome. (Miller et al., "A Crossed Polaroid-Pinhole Device," Ann. Opthalmol., 1986, Vol. 18, 212-15. That study also indicated that a pinhole diameter of 1.6-1.8 would provide better than 20/40 vision even in the face of artificially induced refractive errors of up to 3 diopters. Miller and Johnson also studied the pinhole effect with the hope of solving vision problems. (Miller and Johnson, "Quantification of the Pinhole Effect," in "Perspectives in Refraction," Rubin, ed., Survey of Opthalmology, 1977, Vol. 21, 347-50.) They found that pinholes were useful for overcoming artificially induced refractive errors, and, in particular, that pinholes with a 1.0-2.0 mm diameter were most useful. They revealed a soft contact lens which was dyed black except for a 1.5 mm aperture and which maintained 20/40 vision even in the face of a 6 diopter error, but which constricted peripheral vision. They also revealed a soft contact lens with a clear 1.5 mm pinhole defined by a blackened annulus with an outer diameter of 4.5 mm which was surrounded by an outer clear ring to improve peripheral vision. The present invention takes advantage of the focusing power of the pinhole while at the same time getting around the problem of dim illumination in low ambient light conditions.